Murphy married Pearl Harriett Adams on September 10, 1919. They had a son, Dr. William P. Murphy Jr. Daughter Priscilla Adams died in 1916
In 1924, Murphy bled dogs to make them anemic, and then fed them various substances, and guaged their improvement. He discovered that ingesting large amounts of liver had seemed to cure the disease. Minot and Whipple then set about to chemically isolate the curative substance and ultimately were able to isolate the vitamin B12 from the liver.